Preparation

Preheat oven to 350°F. Combine first 5
ingredients in a small bowl. Place each rack
of ribs on a double layer of foil; sprinkle
rub all over ribs. Wrap racks individually and
divide between 2 baking sheets.

Bake ribs until very tender but not falling
apart, about 2 hours for baby backs and
3 hours for spareribs. Carefully unwrap
ribs; pour any juices from foil into a 4-cup
heatproof measuring cup; reserve juices.
Let ribs cool completely. DO AHEAD: Ribs
can be baked up to 3 days ahead (the flavor
will be more developed, and the cold ribs
will hold together better on the grill as
they heat through). Cover and chill juices.
Rewrap ribs in foil and chill.

Build a medium-hot fire in a charcoal
grill, or heat a gas grill to high. Add broth
or water to rib juices, if needed, to measure
1 1/2 cups. Whisk in barbecue sauce to blend.

Grill ribs, basting with barbecue sauce
mixture and turning frequently, until
lacquered and charred in places and
heated through, 7-10 minutes. Transfer
to a cutting board; cut between ribs to
separate. Transfer to a platter and serve
with additional barbecue sauce.